This invention relates to the preparation of high-strength titanium or titanium-alloy material fasteners. More particularly, the present invention relates to the preparation of high-strength titanium or titanium-alloy material fasteners for use in hybrid fastening systems. The invention further relates to the use of organic, corrosion-inhibiting coatings to pre-coat the high-strength titanium or titanium-alloy material hybrid fastener components.
Various two-piece metallic aerospace fastening systems have long been used for the joining and assembly of aircraft structures and components. Specifically, two primary systems are widely employed in the installation of male and female fastener components. The first system utilizes male threaded pins, which may be installed with female mating components, i.e., either threaded collars or nuts. The second system employs male lockbolts that may be installed with swaged cylindrical collars. Both fastening systems and assembly approaches can be, and have been, automated to various levels over the years. However, the use of such two-piece mechanical fastening systems has several inherent drawbacks, each in their own separate ways.
For example, with the threaded pin fastening system approach, the drawback issue or limitation has been in achieving the fastener assembly/joint integrity and associated strength allowables, which directly result from the application of adequate and proper torque during installations, while not incurring additional expenses associated with the time associated with installing the female threaded nut/collar components. The strength issue can and has been reconciled by the use of stainless or alloy-steel or titanium-alloy material female threaded nut/collar components, which however are heavier though than the female aluminum-alloy material swaged collar components, but the clamp-up/re-torquing issues surrounding the installation of the threaded nut/collar components still can pose cost challenges. Not to mention the problems associated with re-torquing requirements brought on by the use of wet faying-surface sealants. This re-torquing process step has been automated to a certain degree with electrical nut-runners, whether machine-based or manual, but can lack in the ability to achieve adequate clamp-up if not performed in a fully automated assembly machine.
Likewise, the drawback issues or limitations associated with the installation and assembly of traditional pull-type or stump-type lockbolt fastening system approaches deal with the continual challenges of achieving adequate and proper swaging or compaction of the female aluminum-alloy material collar components onto the concentric grooves of the male stump-type or pull-type lockbolt components. Further, rework with the general lockbolt approach can be somewhat expensive, requiring the subsequent cutting and removal of any unacceptably swaged collar component installations. With this rework procedure, once the swaged collar components are successfully removed, the problem of re-swaging replacement female collar components remains since their installations require an extremely large swaging force and repositioning of not only the wing panel assembly in the automation equipment, but possibly the re-installation and repositioning of the specific fastener installation as well.
It is desired to provide a fastening system that combines the advantages of the two systems discussed above, but which avoids the disadvantages associated with either the proper swaging and re-swaging of aluminum-alloy collar components or proper torquing of threaded nut/collar components.